Page:A Treatise on Electricity and Magnetism - Volume 2.djvu/446

 414 MAGNETIC ACTION ON LIGHT. [830.

d 3 and --, o ?, I am n ^ aware that this form of the equations has

��been suggested by any physical theory. The third formula, (III), results from the physical theory of M. C. Neumann 56, jn which the

equations of motion contain terms of the form -=? and --- =f t.

dt dt

It is evident that the values of given by the formula (III) are not even approximately proportional to the inverse square of the wave-length. Those given by the formulae (I) and (II) satisfy this condition, and give values of which agree tolerably well with the observed values for media of moderate dispersive power. For bisul phide of carbon and creosote, however, the values given by (II) differ very much from those observed. Those given by (I) agree better with observation, but, though the agreement is somewhat close for bisulphide of carbon, the numbers for creosote still differ by quan tities much greater than can be accounted for by any errors of observation.

Magnetic Rotation of the Plane of Polarization (from Verdet}.

Bisulphide of Carbon at 24. 9 C. Lines of the spectrum Observed rotation Calculated by I.

II. III.

��Creosote at 24. 3 C.

Lines of the spectrum C D E F

Observed rotation 573 758 1000 1241 1723

Calculated by I. 617 780 1000 1210 1603

II. 623 789 1000 1200 1565

III. 976 993 1000 1017 1041 Eotation of the ray E = 21. 58.

We are so little acquainted with the details of the molecular

tricas vel magneticas declinetur. Halis Saxonum, 1858.
 * Explicare tentatur quomodo fiat ut lucis planum polarizationis per vires elec-

t These three forms of the equations of motion were first suggested by Sir G. B. Airy (Phil. Mag., June 1846) as a means of analysing the phenomenon then recently discovered by Faraday. Mac Cullagh had previously suggested equations containing

,33

terms of the form - in order to represent mathematically the phenomena of quartz. dz s

These equations were offered by Mac Cullagh and Airy, not as giving a mechanical explanation of the phenomena, but as shewing that the phenomena may be explained by equations, which equations appear to be such as might possibly be deduced from some plausible mechanical assumption, although no such assumption has yet been made.

��i C D

�E

�P

�G

�592 768

�1000

�1234

�1704

�589 760

�1000

�1234

�1713

�606 772

�1000

�1216

�1640

�943 967

�1000

�1034

�1091

�Rotation of the ray

�E = 25. 28.

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